On a business trip to Montpellier a while back, I had a day off before heading back home and visited Nîmes, a small city half an hour away by train. Nîmes is known for its Roman heritage and there are some very impressive old sites to behold. Nîmes is a fairly small city in the south of France, which in the Roman era used to be situated along the Via Domitia, a road from Italy to Spain. Several sites from that time have been preserved, including the Maison Carrée (~19 BC) and the Arena (~ AD 70).
Also worth a wander are the 18th century Jardins de la Fontaine at the foot of the Tour Magne, which offers an exquisite view over the city when climbed.
The magnificent historical sites coupled with a vibrant small town vibe makes Nîmes definitely worth a detour. Enjoy!
Also of interest: other European city trip destinations.